The present invention relates to the in situ generation of chlorine dioxide. More particularly, the invention relates to a portable chlorine dioxide generator engagable with a container of aqueous chlorite to generate chlorine dioxide, and to the method of generating chlorine dioxide from the aqueous chlorite.
Chlorine dioxide is used in numerous commercial and industrial applications. Chlorine dioxide provides a microbiological control agent in the dairy industry, the beverage industry, and in the processing of poultry, beef, and other food products. Chlorine dioxide is used as a bleaching agent for paper pulp and other chemical applications. Chlorine dioxide is also used in potable water treatment facilities, in industrial cooling systems, and in the oil and gas industry. Chlorine dioxide is increasingly used in industrial waste treatment facilities because of its selectivity towards environmentally objectional materials such as phenols, sulfides, cyanides, thiosulfates and mercaptans. Chlorine dioxide has rapid disinfection kinetics, is non-reactive with ammonia and most organics, and is effective over a wide pH range.
Chlorine dioxide has been traditionally produced by several chemical processes. For large applications requiring tons of production per day, chlorine dioxide was created with chlorate as the base reactant. For smaller applications requiring less than several tons of chlorine dioxide, sodium chlorite is typically reacted with aqueous chlorine supplied by gaseous chlorination or from the reaction of sodium hypochlorite with hydrochloric acid. Chlorine dioxide is also formed by the reaction of chlorite with acid.
Chemical generation of chlorine dioxide is formed in a special reactor referred to as a "generator". Commercial chlorine dioxide generators are constructed with PVC or other plastics and mix the reactants with positive displacement pumps or with vacuum creating eductors. At least two chemicals are required in the conventional production of chlorine dioxide, and the cost of the generators precludes the economic application of chlorine dioxide to small applications.
Another known technology uses electrolytic processes to generate chlorine dioxide from an aqueous solution of sodium chlorite or sodium chloride. This technology is not widely used due to the size or cost of the generators and the resulting production of explosive hydrogen gas.
The photochemical creation of chlorine dioxide from aqueous chlorite has been reported in the literature for many years. In 1961, Buxton and Williams reported their studies regarding the photochemical decomposition of aqueous solutions of oxyanions of chlorine and chlorine dioxide. In 1962, Kujirai and Fujita reported that ultraviolet (UV) light generated chlorine dioxide, that the rate of chlorite decomposition decreased with increasing wavelength, and that virtually no chlorine dioxide was produced by wavelengths greater than 300 nm.
Other work has been published in the field of chlorine dioxide generation. U.S. Pat. No. 4,414,180 to Fisher (1983) disclosed a central reaction tube containing chlorite solution. The container was bombarded with radiation from externally placed incandescent or fluorescent lamps to create chlorine dioxide. Similarly, U.S. Pat. No. 4,456,511 to Fisher (1984) disclosed a corresponding method for generating chlorine dioxide gas by illuminating the chlorite solution batch and by discharging the aqueous phase chlorine dioxide into the gaseous phase.
U.S. Pat. No. 4,874,489 to Callerame (1989) disclosed a test chamber for generating a batch of chlorine dioxide by subjecting chlorite to ultraviolet radiation. A "shiny reflector" was positioned at the outside of the chamber to concentrate the radiation emitted by the ultraviolet radiation source, and the ultraviolet radiation was discontinued for safety reasons when the chlorine dioxide concentration within the batch chamber reached ten percent by weight. The lamps simultaneously irradiated all of the sodium chlorite solution within each batch and retained the produced chlorine dioxide gas within the chamber. Afterwards, the entire reaction product containing up to ten percent chlorine dioxide was removed from the reaction space.
Chlorine dioxide and certain reactants for the formation of chlorine dioxide have caused accidents and injuries. Sodium chlorite powder is a very strong oxidizer that can flash or explode when contacted with an oxidizable substance such as an organic or cellulose based material. Accidents have occurred in the storage and handling of sodium chlorite, such as when sodium chlorite solution is poured from one container to another, and when dilution pumps do not properly dilute the reactants to safe concentrations. Spills and leaking pumps can permit the evaporation of the solution and the resultant accumulation of chlorite crystals which are ignitable when contacted with organic and cellulose materials.
Because chlorine dioxide can explode when the concentration exceeds a certain level, chlorine dioxide generators should avoid the undesirable accumulation of chlorine dioxide in gas or liquid form. Such generators should avoid the risks associated with transporting and mixing the hazardous reactants used in the formation of chlorine dioxide. Accordingly, a need exists for an improved apparatus and method for producing chlorine dioxide in a safe and economical manner.